Vibe direction

Apologies in advance for asking a low-level (but important) question.

Assuming a random vibe, single-axis screen is performed on a circuit card assembly, what is the optimal direction of vibe?
Case 1 - assume the card has only thru-hole components.
Case 2 - assume the card has only surface mount componets.
Case 3 - assume the card contains both thru-hole and surface mount (mostly surface mount)

Thank you!